In recent years, the number of failures in mobile terminal devices destroyed as a result of being heated by electromagnetic wave radiation equipment such as microwave ovens has been increasing. One reason behind this is that microwave ovens are sometimes used as means for drying wet mobile terminal devices. Based on this situation, mobile terminal devices that record temperature history have been proposed (see, for example, patent literatures 1 and 2).
A mobile terminal device disclosed in a patent literature 1 includes a label, and operates as follows. The label is colored when temperature reaches a predetermined temperature. The coloring is performed by wax or a chemical reaction. Accordingly, it is possible to determine that the temperature has reached a predetermined temperature.
A mobile terminal device disclosed in a patent literature 2 includes a label, and operates as follows. A temperature indicating element of the label is melted and flowed, and black carbon which is in the background is seen in black when the temperature reaches a predetermined temperature. Accordingly, it is possible to determine that the temperature has reached a predetermined temperature.
Meanwhile, other techniques for measuring the temperature of an object to be heated in a microwave oven have been suggested (see, for example, patent literatures 3 to 5).
A packaging container disclosed in the patent literature 3 includes a seal, and operates as follows. The seal peels off when steam pressure in the packaging container increases. In this way, it is notified that heat-cooking of the object to be heated in the packaging container has been completed.
A temperature detector disclosed in the patent literature 4 includes a thermal sensing probe, and operates as follows. The thermal sensing probe detects the temperature of the object to be heated while using microwaves as a power supply. Accordingly, the temperature of the object to be heated placed on a turntable is detected.
A packaging container disclosed in the patent literature 5 includes a seal, and operates as follows. A cutline is provided in the seal, and the cutline is broken when the steam pressure in the packaging container increases. In this way, it is notified that heat-cooking of the object to be heated in the packaging container has been completed.